As others have mentioned, generating less gray water can solve the "plug problem." Random thoughts: Similar to what OpnspaAs mentioned, an adjustable rubber engine block freeze plug; placing a heavy weight over the drain plug; taping the plug down with Gorilla Tape; make a suction cup or velcro bracket to hold the plug in place; line the top of the drain with stair/bathtub traction tape to better grip the plug; run a bead of silicone seal along the top of the drain and push the plug just below the bead; prop a long wooden dowel from the plug all the way to the ceiling; letting the gray water come up and just accept that; running faucets with just a tiny trickle of water and adapting to that; bathing with Walgreens no-rinse soap sponge baths and no-rinse shampoo (very little water); bathing less frequently; bathing outside the camper rather than inside; not washing dishes when feasible and doing so later at home; using plastic/paper utensils and dinnerware; rinsing dishes in a shallow tub rather than under a faucet (less water); diverting cleaning/bathing wastewater from gray drains to down the toilet.
