hi there
personally i would sell it down the following line;
provide item costs for the consumables and that items will be charged on an as used basis, as i have found that contracts that include consumables are always less cost effective for the client. as the contractor will always provide an uplift for consumables over and above what they use.
another point is, that if they are using standard toilet rolls, you could illustrate a saving if they were to install jumbo roll dispensers, similar sell z fold hand towels rather than C fold towels, usage is then less.
rgds
martin
