I owned one of the Rainbow D2 vacuum cleaners from 1974 till 2007 when it finally gave up the ghost after HARD service. Now I realize I could have had it rebuilt but my loss.
So I ordered another exact copy after trying several other brands which just did not hold up to the Rainbow.
The Rainbow D2 is by FAR the most powerful suction of them all and could be controlled with the air block / release on the stem of the extension so you could do curtains and suck up a bolt you dropped in a crevice with one turn of the wrist. I could not do without it any longer. Cannot believe it took me so long.
The water kept any dust particles trapped and could remove allergens from a room in a short time. I never found emptying the canister a problem though I have heard some complaints of it being difficult.
I just dumped it on a stony area outside the house and raked up the dog hair and particles into the garbage when it dried.