After Beary and Henry get into the bus to go get the band, there is a shot of Beary hanging out the window of the side of the bus. In the shot, the bus is clean, but this is before the bus goes through the car wash. The next outside shot of the bus shows it dirty.
When Henry is talking to Ted on the pay phone in the background you see the bus dirty just after they wash then when the bus pulls away once again it is clean just like when it came out of the car wash.
When Fred is in the boat on the way to save the rest of the crew, he turns the corner the boat goes up on one wheel and the two extra wheels underneath that make the stunt possible are briefly visible.