I am about to set a bathtub onto an already installed drain. Before moving the cast iron tub into place I need to first set a rubber washer on drain assembly. Since there is very access and the tub is a beast, I'd like to adhere the gasket in place before moving the tub. Could a put a layer of silicone down under the gasket to glue it in place? 
1 Answer
A thin layer of silicone won't hurt but make sure it is evenly applied in case it takes longer to place the tub and pull the drain tight. Several houses back I was doing a remodel that the original owner used a thick layer and let it dry prior to installing the tub I don't know how many years before but it had a small leak and I had to replace two of the joists and some decking because of the leak, but a thin coating will help seal and hold it in place while setting the tub.
gasket sealantbetween a silicone gasket and a metal piece. It holds the gasket in place, but never dries so you can reposition it. I don't know if this could be used between silicon and whatever material your is. Also of factor, an automotive gasket will be tightly compressed.