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Nine out of ten bidet plumbing questions come down to one part: the T-adapter. It is the small fitting that splits your toilet's water supply so the bidet gets its own line. Get the size right and installation takes 15 minutes. Get it wrong and you are back at the hardware store. Here is how to get it right the first time.
7/8 inch is the connection under the toilet tank, where the fill valve meets the supply line. Almost every modern US toilet uses this size. If you are installing a bidet attachment on a typical American toilet, 7/8 inch is the one you need.
3/8 inch is the compression fitting at the wall, where the supply line meets the shutoff valve. Some installations split the line there instead of at the tank.
1/2 inch shows up on some older homes and commercial plumbing where the supply connection is half-inch threaded pipe.
Look at where the water line connects to the bottom of your toilet tank. That plastic nut threading onto the fill valve is 7/8 inch on nearly every US toilet made in the last few decades. If you would rather split at the wall valve, check the nut where the supply hose meets the shutoff: that is usually 3/8 inch. When in doubt, connect at the tank with a 7/8 inch adapter. It is the standard setup in our installation videos.
The brass T-adapter with stainless steel hose is $19.99 and comes in all three sizes. Metal threads hold their seal for years and tolerate a firmer tightening.
The plastic T-adapter with PVC hose is $14.99. It is lighter on the fill valve and hand-tightens easily, which makes it harder to over-torque. It is the budget pick and the same style included with our standard kits.
If you want the install to be a set-and-forget job, choose brass. If you are outfitting a rental or want the lightest touch on the plumbing, plastic does the job.
A slow drip at the T-adapter almost always means a worn, misplaced, or missing rubber washer, not a broken fitting. Replacement washers are $5 and come in the same three sizes: 7/8, 3/8, and 1/2 inch. Match the washer to your adapter size, seat it flat, and hand-tighten plus a quarter turn.
Every adapter and washer ships with free shipping, 60-day returns, and a 1-year warranty.
7/8 inch. The connection under the toilet tank where the fill valve meets the supply line is 7/8 inch on almost every modern US toilet. When in doubt, this is the size to order.
Usually not. The 7/8 inch tank connection seals with a rubber washer, not tape. If a connection drips, check that the washer is seated flat and not worn before adding anything else.
Yes. T-adapters use standard plumbing threads, so a 7/8 inch adapter fits any bidet attachment that connects at the tank, whatever the brand.
The usual cause is a worn or missing rubber washer. Replace it with a $5 washer in the matching size, seat it flat, and tighten by hand plus a quarter turn. Overtightening can crack plastic fittings.