The act of inserting one's entire penis and scrotum into an anus or vagina. The difficulty of that feat is akin to getting three dogs to take a bath at once, hence the phrase 'three dogs in a bathtub.'
Fitting my whole package into Sarah was harder than putting 3 dogs in a bathtub.

Or:

Kelly was so wide open I put three dogs in the bathtub.
by Slime Church February 24, 2011
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