There are numberous ways to to this without having to buy giant trays:

See-Saw up-and-down in a wall paper wetting tray. A stick attached to opposite edges will aid handling.

OR

Cover a piece of plywood with plastic sheeting then incline it in a sink. Use a spray bottle to apply developer etc. and spread with a sponge. Adding 100% more water to the developer will provide extra control.

Wash both sides using a hose.

Have fun.