Can dishwashing liquid kill sperm

No. There is no good alternative to condums with spermacide. If there was condums would not be for sale (as much as men complain about them.) Yes. Dishwashing fluid has a high enough acidity to kill sperm exposed to the air. It is, however, too toxic to use as a spermacide. Also, sperm can not survive for more than an hour outside the body.