I like this pipe piece. It can be used in 40K, GorkaMorka or Necromunda, and is one of the easiest pieces on the site to make.
MDF or plywood for the base, and sand to cover it.
A 90 degree bend 2 1/4 inch waste pipe section, and about 9 inches of straight waste pipe.
One plastic bracket (the ones which fix the pipes to the wall)
Hot glue gun
Chain-link fencing and barrels for decoration (see relevant TerraGenesis section).
PVA wood glue (the white stuff)
Cut a base about 12 inches long by 5 inches wide
Cut the straight pipe section to the required length, and cut the exposed end into a ragged shape to look like a broken pipe.
Push the bent and straight pipe sections together and hot glue-gun them to the base.
You'll have to build the bracket up because it won't reach the base. I glued some plastic blocks to the base under the bracket. On another model I did away with the bracket and used a block of wood to support the end of the pipe.
Use the hot glue gun to create dribbles of goo oozing out of the end of the pipe or from cracks along its length.
Embellish the base with barrels and chain link fencing.
Cover the base with PVA and then sand.
I cut some cracks into the pipe on one side and added some hot glue-gun ooze. Be sure your first dribble of glue has gone really cold, otherwise the next squirt will melt it again.
To make hot glue-gun ooze squirt the glue and then blow like crazy to make it set in a dribble.
Spray the model black. Dry brush the pipe up in silver, bronze, brass etc. Wash liberally with Chestnut Wash diluted 50/50 with water. Use neat wash to get strong staining here and there. I add the sand to the base after spraying the rest black - sand is easier to paint if you just paint it without priming it first. Give it a good coating of well watered down Snakebite Leather and then dry brush up with light browns, yellows and white. Add further washes when the drybrushing is dry to make pools of stained, dirty liquid.