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zinniachick 07-14-2008 10:03 AM

drill hole in new sink
Hi all -- I'd like to drill a vent hole in my new bathroom sink. It came (as per my order) without one. D'oh. It drains slowly, unless I stick a drinking straw down through the full-of-water sink to the drain hole, then it drains beautifully.

Am I nuts to try it? The sink is made of whatever composite most new sink/countertop seamless units are.

What drill bit would you use?

RippySkippy 07-14-2008 10:26 AM

I don't understand, where are you thinking you would drill the hole to allow air in?

majakdragon 07-14-2008 11:34 AM

Sinks do not have vent holes. Bathroom sinks are available with or without an overflow hole and I think this is what you are talking about. You have a pipe problem, not a sink problem. Your sink piping may not be vented.

zinniachick 07-14-2008 12:53 PM

Majakdragon, you're right -- overflow hole. I don't have one. But, to answer RippySkippy's thought too, doesn't the overflow hole flow into the drain, thereby providing an additional vent for that drain? The sink drain does connect to the main bathroom vent, it just seems to need more air flow to allow the water to flow out smoothly.

So I'm thinking of drilling an overflow hole, just a little quarter-inch diameter hole, where one normally would be. What do you all think? Thanks for your replies.

majakdragon 07-14-2008 01:28 PM

Bathroom sinks are "double walled". The water that goes through the overflow holes goes inbetween the walls and into the drainpipe. The pipe used for sinks with overflow holes is different than those without. There is an opening just below the flange in the sink to allow this water to enter the piping. drilling a hole in the sink will not help your problem and could break the sink in the process. Go to a Home Center or hardware and look at sink drain assemblies and you will see the difference.

zinniachick 07-14-2008 02:05 PM

Thank you -- that's what I wondered, whether it was as simple as putting a hole in, or whether there was a big reason not to. Any way to tell whether my sink is made for an overflow hole or not? Could it be that they make only the one kind and sometimes don't drill the hole, at the customer's request? Or is this purely wishful thinking? I can crawl under there and look up, but what would I be looking for?

majakdragon 07-14-2008 02:42 PM

The body of the sink is cast and the hole is added in the casting. Then porcelain coating is added and baked on. Yours may, or may not be double walled. With the advent of people wanting Vessel sinks, the overflow was deleted to many designs. This is one of the reasons I stated the problem was piping and not the sink. The drain opening in the bottom of a vessel sink is the same as what you have and there are no "vent" holes. Thus, your problem is piping related.

zinniachick 07-14-2008 06:30 PM

Say, MD, I sure do appreciate you taking the time to explain this to me. So, how best to address the need for more air inflow into my drain pipe? It really does seem to be exactly that; the toilet, shower and tub all drain beautifully, and all use the same vent pipe as this sink. By the way, it's a double sink, both bowls having the same trouble.

Is there another flange and drain pipe assembly I could switch out for? I'm sure it's not clogged, it just wants air exchange and can't get it. What the devil was I thinking when I said no need for an overflow hole?!

DUDE! 07-14-2008 06:46 PM

not a plumber, but it seems you have some blockage there. I'd take off the trap and have a look inside.

majakdragon 07-14-2008 06:49 PM

Is this a new sink installation with the new sinks installed where there was no sink before? since it is a double sink, put water in the one closest to the toilet. Reason for this is that the main vent is probably behind this toilet. Now try draining the water. The other sink is tied into the same drainline and the drainhole in this sink should serve as a vent for the other sink. If this doesn't work, I would suggest you disconnect some piping under both sinks and see if there is something blocking the line.

zinniachick 07-14-2008 06:54 PM

Well, you two make a good case. I'll pull apart the traps and see what I see. This is a new double sink replacing an old double sink, and there was a massive block in the drain where it entered the wall, which my saintly contractor tore out and dredged clean for an entire afternoon. The sinks have been in place for a couple of years now. Both drain equally slow, and have always drained a little slow, while all other drains in the bathroom and the kitchen on the other side of that wall drain like God and nature intended. The shower, tub and toilet also were replaced when the sinks were.

RippySkippy 07-15-2008 08:57 AM

1 Attachment(s)
In addition to the blockage and the sink has a built in vent/overflow passage; it's possible the original installers used a drain tube without the over flow holes.

In the attached image, notice at the difference between part 1025639 (circled on the left) which is the "typical" drain tube, where 1032296 is the drain tube for the vessel type sinks. Before dismantling the sink, I'd verify which type of sink you have and make sure it has the correct drain/overflow tube. It's possible to replace that piece and not the whole drain assembly. Check on Ebay.

majakdragon 07-15-2008 09:23 AM

RippySkippy's drawing shows what I was talking about in my previous post (at 1:28). The drain (circled part) on the left has holes near the top and is for sinks with an overflow. The other circled pipe (on the right) does not have holes and is for sinks without overflows.

zinniachick 07-15-2008 11:11 AM

I understand what you're saying, but I don't understand why it matters; if the drain pipe has the overflow holes, and the sink has no overflow, nothing will ever come to the holes, not even air to help with drainage. If it doesn't have the overflow holes, then... it's the right pipe for this sink, which is similar to a vessel in that it has no overflow. Is my assumption correct? Thanks for digging up that great illustration.

And thinking perhaps outside the confines of good sense, would installing a vertical piece of pipe that had a very tiny Y, so it could gasp air and help drainage (assuming I don't have a clog, which I'll check before proceeding)... would this be folly? As long as it's above the trap and doesn't allow sewer gas into the house?

majakdragon 07-15-2008 11:49 AM

Hmmm, let me try to explain this. If you had a sink with the overflow hole, the bottom of the sink is built to allow the double walled sink discharge hole to line up with the pipe that also has drain holes in it. When the sink is full of water, these holes are immersed in water and do not serve as a vent. This is the same as your sink with no overflow. If your sink had the overflow holes, and you used the pipe with no holes, you would be blocking the flow of water from the overflow. If you had no overflow and used the pipe with overflow holes, it would leak out of those holes since the vessel type sinks do not have room in the bottom to cover the holes. You either have a clogged pipe or the ventpipe to the sink was disconnected when the sinks were installed. Adding anything to aid in draining, such as the Y you talked about would do no good and would also leak water when the sink was used. Your first post that stated the drain worked fine by sticking a straw down the drain hole tells me the vent was disconnected. (even though it shouldn't since the trap would still be full of water)

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