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Old 07-13-2008, 03:30 PM   #1
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replacing old galvanized drains


i have to replace the drain for the tub and sink in a bathroom. both drains are old galvanized drains that are rusted shut. they both tie into the main stack at the same height on opposite ends of each other. ( the tub is to the left of the toilet and the sink is to the right). i am hoping that the fitting in the main stack where they tie in is ok so all i have to do is cut the drains near the stack, use a rubber connector, and run pvc out. the only vent is the main stack itself. do i have to put in additional vents now or is it ok to have only the stack vent? also if the fitting itself where the drains tie in, is rusted shut too(i have not yet cut the drains out), how do i replace that fitting?
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Old 07-13-2008, 07:02 PM   #2
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replacing old galvanized drains


Cut the galvanized pipe about 4in short of the stack. So long as the galvanized pipe isn't rusted through or breaking off at the threads it should be fine to tie into with a no hub clamp. If it's full of crud just dig it out with a screwdriver or something, try not to drop it into the stack though. Should you have to change those fittings you need to support the stack so it doesn't fall, cut out a section, and replace that section with PVC and new fittings.
As for vents by code you need to vent them individually. If at all possible I would do that.
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Old 07-13-2008, 10:37 PM   #3
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replacing old galvanized drains


you mean vent the tub and the sink separtely? do i have to stick two new vents out of the roof then or can those two vents come together and then just have one new vent going out to the roof.
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Old 07-14-2008, 02:40 AM   #4
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replacing old galvanized drains


Yes, the tub and the sink both need to be vented after the traps.
No, you do not have to vent them out of the roof...just into the main stack that is already going out the roof.
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Old 07-14-2008, 06:17 PM   #5
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replacing old galvanized drains


the main stack is cast iron. so somewhere above where the drains enter the stack i should cut in it and put a pvc t for the vents to enter from either side? its an old house is it against code to leave it the way it is?
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Old 07-14-2008, 10:00 PM   #6
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replacing old galvanized drains


If you don't touch anything then it isn't against code. If you re-pipe the lines then you need to ad vents. It's not like the plumbing police aren't going to come and arrest you if you don't. Chances are you will never have a problem inspection wise. You may have drainage issues though.
Yes, you would need to cut out a piece an add a tee. The stack is heavy and if it isn't supported it can fall. Sometimes stacks are only supported from the bottom so you need to put some riser clamps or something on there before cutting it. If you are only adding a tee and not replacing an entire section I would use a cast iron no hub tee to tie the vents it.

Last edited by Marlin; 07-14-2008 at 10:03 PM.
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Old 07-14-2008, 10:11 PM   #7
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replacing old galvanized drains


when you say after the traps, does that mean the vent would extend up leaving the drain closer to the tub than the trap, or closer to the stack than the trap? also today i cut the pipes within 4'' of the stack like was suggested. the tub drain was ok, i cleaned it out with the screwdriver and seems to be ok. the sink drain though was completely rusted shut. should i try to grind it open, or use a pipe wrench to remove it from the hub and replace it with a new piece of galvanized. also instead of revented to tub and sink, is it possible to leave the tub a wet vent and for the sink add one of those dummy vents?
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Old 07-14-2008, 10:21 PM   #8
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also if i do decide to vent to correct way, this bathroom is on the second floor, so, above where i cut into to main stack, there is only about six or seven feet before the roof, so would it just be easier to replace this whole top section with pvc as oppossed to cutting the stack twice and support the upper section with supports? and if this is better, what do i put over the pvc stack above the roof, anything or do i just leave a white piece of pvc sticking out? (im always looking at the older houses, they look way cooler than the new ones)
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Old 07-14-2008, 10:36 PM   #9
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The vent goes closer to the vent then trap.

You could try unspinning the nipple. You need a 24" or a 36" wrench or you don't have a chance though. Their is also the possibility of it snapping off at the threads. As for grinding, it may work but you would need to be careful not to drop too many rust chunks down your stack.

It may be more feasible for you to just cut the stack below those fittings and re-pipe from that point up in PVC. That way you're done for good with the galvanized and you're properly vented except for the toilet which I'm betting doesn't have a vent either. The only thing is you might have to replace the roof flange or at least put some flashing cement around it when you're done if you disturb it. I'm not the one to ask about roof flanges, I don't go up there.
Most people just leave the white PVC going out the roof. I always either paint it black or use a no hub clamp to transition to cast iron the last 30".
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Old 07-14-2008, 10:43 PM   #10
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replacing old galvanized drains


yes i have been thinking about replacing the whole hub and toilet drain with pvc. isnt the main stack itself the vent for the toilet? also i read about heating the hub and putting bees wax on it so it gets sucked into the threads and acts as lubricant, does this work? maybe i should try this and if i run into problems then ill just replace the whole hub with pvc.
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Old 07-15-2008, 08:21 AM   #11
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replacing old galvanized drains


alright one last question about this bathroom. if i decide to cut the stack below the hub to replace it all with pvc, (this bathroom is on the second floor) in the room below, i will have to open the wall to get to it, should i cut closest to the floor in that room right above the basement (i will have more metal for scrap) or should i cut closest to the ceiling to cut down on the noise of the drain. or maybe my reason for leaving the most cast iron is bad. should i replace as much as possible so there will be less pipe that may rust through some day?
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Old 07-15-2008, 02:48 PM   #12
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Cast iron especially on the vertical lasts a long time. I cut out cast iron stacks that are 80 plus years old that look just fine on the inside, in fact the older cast iron is heavier than the stuff they use today. No one can make any guarantees about your situation without physically going to your house and seeing what you have though.
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Old 07-15-2008, 03:41 PM   #13
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replacing old galvanized drains


i have decided to grind out the sink drain to attach pvc leaving the main hub in place. then i will run two new vents up, one above the sink and one above the tub, connect them in the attatic and run it out the roof so i dont have to cut into the main stack. i think it will be easier to run a new 2'' vent out of the roof.
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Old 07-16-2008, 04:51 AM   #14
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replacing old galvanized drains


Most places require you to increase to 3" going out the roof. You might as well just use a pro vent if you aren't going to cut into the stack though.
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Old 07-16-2008, 11:41 AM   #15
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what is a pro vent? the vents are going to be 1 1/2'' each, so then when i connect them before going out of the roof, i should increase to 3"?
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