I'm talking mostly about late wave situations on endless here. I usually start to have problems with this combination around wave 40 or so (casual difficulty, but playing solo).
I've finally figured out how to handle some of the waves that have given me problems in the past - Walker/Tank, Walker/Soaker. To handle Walkers I usually get them to bunch up by walking backwards in front of them and alternating slows and grenades. With a couple of mortar towers that works well. If there are Chargers or Runners with them then the tactic works for those groups as well. Since the tactic for Tanks and Soakers is to keep them separated so that Lightning/Gatling/Scatter Laser towers hit all of them it throws things off, but I've found that if I just let the walkers get through the first turn or two of my maze before clumping them then they have enough of a lead on the slow moving Tanks or Soakers that they don't start to get bunched with them and I can finish off those guys at the end.
The Big Walkers move faster than the Walkers though, so I can't use that tactic. Any suggestions?
In typing this I'm thinking that I might be able to concentrate on the Big Walkers and then clump the Walkers after the Big Walkers are mostly dead, but I don't know if I'd be left with enough time to finish off the Walkers. Has anyone tried that tactic?