Birchmeier 15 Liter Iris Backpack (4 gallon) 2 Year Manufacturer"s Warranty. Completely rebuildable. Birchmeier is the Best Backpack. Period! Stainless steel base. Rebuildable brass spray valve with brass spray tip. This is a professional grade product designed for many years of service. 4-gallon tank is perfect for most users. Birchmeier is the choice of pest, weed and landscape professionals that know the difference.