Green’s Dictionary of Slang

whoof in v.

also whoomf in
[echoic]

to push something in(to).

[UK]W. Hall Long and the Short and the Tall Act I: Stick it in!... Just close your eyes and whoof it [i.e. a bayonet] in!
[UK]Indep. Traveller 25 Sept. 1: He whoomfs in a quadruple slug of cachaca, a sugar-cane spirit.