Was told to allways run my TM at full revs by the Supplier, also on the TM forum i was told that running at less than full revs can put extra strain on the Rubber Drive couplings (ours is Hydramaster yours may differ but cannot see why). we had some shatter the other day and unless you have spares this takes you out of action. If you worried about to much vac there is a vacuum relief valve on the tool that you can use.
We cleaned loads of draylon with the handtool, using MS, always come up well.
Dene