Shipping with USPS priority tubes

[smithssunshineorchids]

I'm trying to ship some items using the USPS Priority tubes (triangle boxes).  But, I can't figure out how to put them in on the "purchase postage" page.  They don't list the Priority tubes as an option.  So, I always end up going to the USPS site and buying the postage there, which of course costs more than if I purchased it on ebay.  Any help would be greatly appreciated.

Thanks.

[nobody*s_perfect]

It's just a basic 'Package/thick envelope," which goes by the regular rates that are based on weight and distance.  There is no special category for that box (as there is for flat rate and Regional boxes).