I bought some hand-spray bidet kits to add to some toilets. I've done this before on standard toilets, and the installation went smoothly - just remove the input pipe from the port on the underside of the toilet tank, insert the provided T-valve, and connect the hand-spray pipe to the T-valve.
But in my new house, I have some toilets that are non-standard (Porcelanosa NK One) and which do not give access to the input port on the back of the tank. The toilets are fixed to the ground and flush with the wall, and so there is no good access to where the input pipe connects. I can squeeze my hand back there and kind of feel it, but certainly could not unscrew anything and install new plumbing there.
As a result, I am stuck with trying to Tee off the other end of the input pipe - the part that comes out of the wall. The pipe size is different than that on the bottom of the toilet port - the wall valve seems to be a 3/8" compression valve, compared to the 7/8" valve at the input port of the toilet tank. So I cannot use the T-valve that came with the bidet kit.
My question is this - can I just buy an off-the-shelf 3/8" T-valve, insert it between the existing shut-off valve and the input pipe that runs up to the toilet, and connect the hand-sprayer to that T-valve?
Is there any reason such a T-valve will be unhappy having a hand-spray attachment on it? Will the pressure be significantly different at the end of the hand-spray attachment? It won't have the on-off valve that the provided T-valve does, but I never use that anyways (and if I did need to turn off pressure to the hand-spray - say, to remove the end and de-scale it - I could just turn off pressure to the entire toilet).