After high school phys ed swimming was a 40 minute lunchtime and I lived about 12 blocks from home. The bicycle ride home was not enough to unshrink my scrotum. Going straight to the bathroom and doing a super quickie, I still got the extra thrill of shooting through cool vessels.
The cool vessel extra thrill was repeated on bivouac during army basic training. The hot summer forced us to train at night and sleep during the day. There was a stream with cool water so in my swimming trunks, I got in the water for a swim. The rest of the troops were sleeping, I saw no one around so I played for a while with my trunks around my knees. After a while, I discovered it was safe enough to climax through my cooled vessels while under water. The threat of someone catching me was an extra reward that did not happen.