The default setting of the "Submit your work(s) to Tumeng" checkbox on the illustration upload page is off. If you complete the submission process without checking it, your work will not be posted on Tumeng.
If you check it once and have completed posting your work, the next time you go to the illustration upload page, the checkbox will be checked and your work will be posted on Tumeng when you complete the submission process.
Once the checkbox was turned on due to the above actions, if you uncheck it and complete posting your work from the illustration upload page, the check box will be set to off the next time you go to the illustration upload page. And the work will not be posted on Tumeng unless you check it again.
If you have only edited your work, or if you have checked the "Submit your work(s) to Tumeng" checkbox but have not completed the submission process, or if you have set up your work to be posted from the Manage Tumeng linkage page, the checkbox setting on the illustration upload page will not be affected.
Please note that in order to post your work on Tumeng, you must first link your pixiv account with Tumeng. For more details on how to post your work on Tumeng, please confirm here.