How many sites do you have ? You only need to submit a sitemap once for each site because all you are doing is submitting it's URL. Google will come by and crawl the sitemap whenever they think it might have changed. You can specify your sitemap URL in your robots.txt and good crawlers will find that and follow it. Apparently, there is a ping service offered by some search engines...
From what I've read, the best way is to add your sitemap to your robots.txt file. i.e., bash-2.05b$ cat robots.txt SITEMAP: yourwebsite/sitemap.xml This way, the next time your site is spidered, the index will be used. Although the large search engines prefer you to use their web based interface, as they say they will give you feedback on any errors you might have in the map.
I use this site map script and everytime i update my site i create a new sitemap, which pings Google and gets the google bots back. http://enarion.net/google/
Hello, Once you have a sitemap.xml file created you can submit it to Google through the Webmaster Tools (need to log into your account). If you do not see the Webmaster Tools in your account area, then go to About Google, then Webmaster Central to find the link. With regard to creating your sitemap, the best way to do that is that we use a sitemap generator that creates the sitemap in 4 versions (XML, ROR, HTML and TXT), you can setup a cron job to run it once a week or whatever frequency you wish. Once it runs it pings yahoo (requires Yahoo API code) and Google. Its been working like a charm for us. Hope this helps.
I hope you are finding this http://google.com/webmasters/sitemaps/ping?sitemap=http://www.yoursite.com/sitemap.xml
Use Wordpress and get a Sitemap generator Plugin. That will solve all your sitemap problems automatically. I install a sitemap plugin with every new WP site I make, and have never actively thought about my sitemaps. If you manually submit sitemaps, you are waaaaaay behind the curve...