which bands was he a manager for?
The Pretty Things and Pink Floyd
Peter Watts (road manager)
Watts was the road manager for The Pretty Things before joining Pink Floyd as their first experienced road manager. 
who is laughing in dark side of the moon Peter Watts who was he? An English road manager and sound engineer
wiki:916409
Peter Watts (road manager) [SEP] Career
Watts was the road manager for The Pretty Things before joining Pink Floyd as their first experienced road manager. Alongside fellow roadie Alan Styles, he appears on the rear cover of Pink Floyd's 1969 album "Ummagumma", shown with the band's van and equipment laid out on a runway at Biggin Hill Airport, with the intention of replicating the "exploded" drawings of military aircraft and their payloads, which were popular at the time. On the 1973 album "The Dark Side of the Moon", he contributed the repeated laughter during "Brain Damage", also heard in the album's overture, "Speak to Me". His wife Patricia 'Puddie' Watts was responsible for the line about the "geezer" who was "cruisin' for a bruisin used in the segue between "Money" and "Us and Them", and the words "I never said I was frightened of dying." heard near the end of "The Great Gig in the Sky".