Farington resident Bill Fairman had the same question when inspecting the work being carried out by Miller Homes on land off Croston Road, Farington.
Mr Fairman had been vocal in his objections to the plans for 175 homes on the land, with worries about flooding high on his agenda.
When he saw the workmen on site carrying out the excavations, his concerns were piqued once more.
He said: “At the public enuiry I mentioned flooding specifically and was poo-pooed.
“Now massive sink holes have been built for drainage tanks, with what look like big plastic toilet roll holders.
“If there isn’t a problem, why is this necessary?”
A spokesman for Miller Homes the sink hole structures are in fact surface water attenuation tanks.
He added: “The installation of water management systems to cope with surface water run-off from new home developments or local highways is a standard practice on all new developments.
“It is not an indication that there are any concerns about flooding but form part of the site’s drainage strategy as agreed during the planning process.”
The development off Croston Road will include a mix of two, three and four-bedroom properties, including a number of bungalows.
The 175 homes will be built alongside community green space, a children’s playground, a cycle and footpath, and part of a new link road running through the site, from the Flensburg Way roundabout.
The six-hectare site is part of a wider area allocated for new homes under South Ribble’s local plan. It is also one of the areas identified under the £434m City Deal.