How many swordtails do you have already and their individual genders?
Swordtails can produce huge numbers of fry (30+ are not that uncommon) so you must make sure you know you have posible homes for this many fry in the chances that you do end up with so many.
May i ask why you want to breed swordtails in particular?
For raisng swordtail fry, i suggest you grab yourself a nice 10gal and get it cycled, thats if you want to breed swordtails seriously- breeding nets/traps are only good for very small numbers of fry and letting the fry fend for themselves in the main tank usually ends up with large losses of them.