In our company on the -400 when more than 150 ton of fuel is required the HST is used.
If any HST fuel is required a minimum of 3,200kgs must be loaded.
During cruise when the Centre Wing Tank (CWT) qty reduces to 36.5t we transfer fuel from the HST to the CWT.
For info the CWT holds 64,973 lts / 52,162 kgs.
All up the -400 can be loaded up with 216,390 lts / 173,740 kgs.