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Author:
taowasam (WA)
My bathtub is a free-standing acrylic tub with an integrated overflow drain slot near the top. If the tub is filled the overflow drains basically nothing but if you keep filling it to basically the top of the tub (1 inch above the overflow slot) and wait about 3-5 minutes it will start draining very quickly.
The tub drains normally and the vent stack has been cleaned out. The overflow drain line also is clear and if water is forced down the line it flows freely. There is about 2 feet of pipe before the U-trap below the tub and then it joins a common drain pipe with the shower which has its own U trap as well and then about 4 feet to a vertical drain stack.
The vent, drain, overflow lines appear to be clear but for some reason it needs about 1 inch of water pressure to "prime" and about a few minutes before it does anything. Which makes it pretty useless as an overflow.
Does anyone know what to look for or fix?
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Author:
hj (AZ)
The overflow probably has a very "narrow' opening, and when water covers it the air in the overflow is trapped, preventing drainage, until the water pressure eventually gets rid of some of the air.
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Author:
taowasam (WA)
So is there nothing that can be done to fix it as the overflow is a integrated part of the tub and the mfg keeps saying it works just fine it just can't handle unlimited flow rate into it. But it clearly does not drain anything initially.
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Author:
KCRoto (MO)
Since the overflow is before the P-trap, a sharp drill bit to make a small hole in the top of the overflow would stop the air lock and wouldn't allow sewer gas, but I am not familiar with the tub itself to know if that is a feasible solution.
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Author:
taowasam (WA)
Not sure if the tub overflow is built into the plastic all the way to the top of the tub I'd have to flip the tub upside down to see how the structure is. It definitely seems like a siphon as it can be started by briefly using the main drain to get the siphon going.
The drilling a air relief hole should be the same as sticking a tiny flexible tube down the overflow to test correct? I think the other problem may be that the overflow channel down to the drain is a thin flat rectangular channel which may easily trap air bubbles with the surface tension of the water flowing down.
The same model on the tub mfg's website no longer has this tiny slit overflow but a normal circular cap and piped one.
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