"I'm just brassed off. It takes a lot to get that stuff back."
He was unsure if the loss will be covered by insurance and will be posting a reward on the store's Facebook page.
It was the first time anyone had used the pipe to gain access to the store, he said.
"We get the normal shoplifting things. We catch some but there's some we don't catch. We can't put the wall right up because of the sprinkler system.
"We are working with the landlord to see what we can do."
The burglar appeared to have exited the building using the same method. The Queen St door to Mastermall was found unlocked.
Anyone with information should contact Masterton police on (06) 370 0378 or call Crimestoppers anonymously on 0800 555 111.