an improved gas baffle device is disclosed for use in on - site waste disposal system tanks , such as septic tanks , which can be adjustably mountable to the outlet line of the septic tank . the gas baffle device includes a mounting strap which is readily secured to a pipe extending downwardly from a sanitary tee mounted the tank &# 39 ; s outlet line . the mounting strap carries a support post and a gas baffle plate . the baffle plate is maintained over the end of and at an angle to the opening of the sanitary tee pipe . special connection means on the strap allow the support post to be readily interconnected thereto . this improved gas baffle device is easily and quickly field - installed into a new septic tank , or can be readily retrofitted into an existing septic tank as needed .