Has anyone any idea how to fix sagging drawer bottoms (no jokes about stronger elastic please!) Duct tape and suchlike only last a few weeks before sagging again
If they are made from hardboard you could try replacing it with plywood or if you don't want to take it apart get some upholstery webbing. Staple and stretch it across the bottom. A couple front to back and maybe one across the width should do it.
I use cable clips (the plastic clips used to fasten cables in place on a wall, etc).
They work fine for me. I put about 5 or 6 just under the sagging wood. Just make sure you use the correct size though, 'cos if you use one with the nails that are too long, they'll go right through the wood and stick out of the other side, although if it's at the back of the drawer, it's not a major problem.
After glueing the drawer bottom into the grooves, glue some wood battens to the underneath across the shortest dimension.Make sure that the wood is thin enough to clear the carcasse.
I would suggest that if it isn't feasible to dismantle the drawer then simply cut a piece of 1/4" thick plywood to the inside size of the drawer and let it rest on top of the sagging bottom.
A small bolt with a countersunk head fitted through the centre of both bottoms would also improve the situation.