Neighbour wants to know. The septic tank people told her, she need a gate to access the backyard for the ditch digging machine. But what size gate should she buy. Maybe they use small excavator to dig the trench?

Yes, they may have a small one. They may have a medium size one. They may even need a lift truck in. This is only a question that the sewer company will know. They need to contact the sewer company and ask what size. Also, how does the pump truck get to the septic to clean it out?

Is she having work done on an existing septic system? Has she selected a contractor? Lots of questions about all this.
For a one time operation, removal and re-installation of enough fencing to access the work would be the standard method.
If he has already signed a contract, access should have been covered in the contract. If the contractor bid or presented a quote to do the work, how did he plan on getting in there?
Or as chuck suggested, is a gate needed for periodic access to pump out?
Maybe there are details you or she left out that explain all this, but sounds a bit screwy to me.
Contractors temporarily remove and re-install fencing all the time.

Is she having work done on an existing septic system? Has she selected a contractor? Lots of questions about all this.
For a one time operation, removal and re-installation of enough fencing to access the work would be the standard method.
If he has already signed a contract, access should have been covered in the contract. If the contractor bid or presented a quote to do the work, how did he plan on getting in there?
Or as chuck suggested, is a gate needed for periodic access to pump out?
Maybe there are details you or she left out that explain all this, but sounds a bit screwy to me.
Contractors temporarily remove and re-install fencing all the time.

They told they wouldn't want to take apart her chain link fence. A gate
Would be more beneficial. It is not the septic tank, it is the drain-field. The machine is like a back hoe is not very big. Perhaps a 36" wide gate would be okay.

I am with smearcase, a gate would be for regular usage. This sounds like they are putting in a whole new fiel which might happen every 50 years.

If it is her responsibility, and she doesn't need a gate ( I think it will need to be more than 3 feet for any backhoe I have seen), she can contact a fencing company and get estimates for a) removing enough fence to give them access and coming back to re-install; and b) installation of a gate. Then take the best option. That assumes that she doesn't need a secure fence 100% of the time for option a. I don't understand why they would tell her she needs a gate and not specify the width they need for their equipment. But that unknown would make it more reasonable to just have a temporary opening available. She wants you to tell her what size gate that her contractor needs? They could have a 10 foot wide (or even wider) CAT backhoe for all you know.

If it is her responsibility, and she doesn't need a gate ( I think it will need to be more than 3 feet for any backhoe I have seen), she can contact a fencing company and get estimates for a) removing enough fence to give them access and coming back to re-install; and b) installation of a gate. Then take the best option. That assumes that she doesn't need a secure fence 100% of the time for option a. I don't understand why they would tell her she needs a gate and not specify the width they need for their equipment. But that unknown would make it more reasonable to just have a temporary opening available. She wants you to tell her what size gate that her contractor needs? They could have a 10 foot wide (or even wider) CAT backhoe for all you know.
Thank you so much

pastor,

You are a real asset to folks down there. Best wishes to you!