Gas odor reported by tenant, who pays for the gas company check?

[Megan Frank]

A week or so ago our tenant reported that the basement smelled of gas and they were worried there was a leak. We instructed them to call the emergency line for the gas company and have them come out. They did and the smell was methane coming from a toilet they let dry out. They poured some water in the toilet and the smell went away. The bill for the gas company coming out is $135. Are we responsible for this as landlords or are the tenants responsible for the bill? The lease states they pay for gas and they have an account set up with the company that came out but the lease does not specify who would pay in this instance. Normally I would probably pay the bill and be thankful that they called the gas company and did not let the house burn down, but these same tenants ran up a $2100 water bill for a running toilet in the passed few months. We were kind in that instance and paid for half of the bill even though the lease states they pay water. This is obviously killing the cash flow for the house. What would you do? Thanks!