Capful of Purex, capful of Calgon, a packet of your favorite tank treatment (Potty Tabs, TST, Aqua-Chem, whatever,) and 5 gal of water. Sloshing is a word, btw, and it's your friend in this case...
That's my treatment for every tank every time, not just for "slosh cleaning" while underway.
2015 XLR Hyperlite 30HFS5 (mods being performed regularly)
2009 Salem LA 292fkds (gone)
Nights- ('12)23 ('13)23 ('14)15 ('15)31 ('16)25
2014 Harley Davidson FLHX (XLR cargo)
2014 VW Jetta TDI (diesel sipper, camping support vehicle)
2011 Ram 2500 CC 4X4 CTD, B&W Companion (toy hauler hauler)