I have a monobloc tap but its footprint is too small for the hole in the sink i,e, it is able to slip into tyhe hole in some positions. I have tried loads of sealant to try to stop it moving around but to no avail, everytime I tighten the locknut up it eventually moves on the sink. There is no large washer under it just an o ring which is the same size as the hole in the sink. I called the supplier, bathstore, and their technical said it is a common problem with these taps so any ideas or is it just try another tap?